Photocatalytic hydroxylation of benzoic acid in aqueous titanium dioxide suspension

Imatinib: Major photocatalytic degradation pathways in aqueous media and the relative toxicity of its transformation products

Imatinib (IMA) is a highly potent tyrosine kinase inhibitor used as first-line anti-cancer drug in the treatment of chronic myeloid leukemia. Due to its universal mechanism of action, IMA also has endocrine and mutagenic disrupting effects in vivo and in vitro, which raises the question of its environmental impact. However, to date, very little information is available on its environmental fate and the potential role of its transformation products (TPs) on aquatic organisms. Given the IMA resistance to hydrolysis and direct photolysis according to the literature, we sought to generate TPs through oxidative and radical conditions using the AOPs pathway. Thus, the reactivity of the cytotoxic drug IMA in water in the presence of OH and h+ was investigated for the first time in the present work. In this regard, a non-targeted screening approach was applied in order to reveal its potential TPs. The tentative structural elucidation of the detected TPs was performed by LC-HRMSⁿ. The proposed approach allowed detecting a total of twelve TPs, among which eleven are being described for the first time in this work. Although the structures of these TPs could not be positively confirmed due to lack of standards, their chemical formulas and product ions can be added to databases, which will allow their screening in future monitoring studies. Using the quantitative structure-activity relationship (QSAR) approach and rule-based software, we have shown that the detected TPs possess, like their parent molecule, comparable acute toxicity as well as mutagenic and estrogenic potential. In addition to the in silico studies, we also found that the samples obtained at different exposure times to oxidative conditions, including those where IMA is no longer detected, retained toxicity in vitro. Such results suggest further studies are needed to increase our knowledge of the impact of imatinib on the environment.

Modeling the photochemical transformation of nitrobenzene under conditions relevant to sunlit surface waters: Reaction pathways and formation of intermediates

Nitrobenzene (NB) would undergo photodegradation in sunlit surface waters, mainly by direct photolysis and triplet-sensitized oxidation, with a secondary role of the *OH reaction. Its photochemical half-life time would range from a few days to a couple of months under fair-weather summertime irradiation, depending on water chemistry and depth. NB phototransformation gives phenol and the three nitrophenol isomers, in different yields depending on the considered pathway. The minor *OH role in degradation would make NB unsuitable as *OH probe in irradiated natural water samples, but the selectivity towards *OH could be increased by monitoring the formation of phenol from NB+*OH. The relevant reaction would proceed through ipso-addition of *OH on the carbon atom bearing the nitro-group, forming a pre-reactive complex that would evolve into a transition state (and then into a radical addition intermediate) with very low activation energy barrier.

Photocatalytic degradation of aromatic pollutants: a pivotal role of conduction band electron in distribution of hydroxylated intermediates

The modulation of the yield distribution of intermediates formed in the photocatalytic degradation of organic pollutants is of extreme importance for the application of photocatalysis in environmental cleanup, as different intermediates usually exhibit distinct biological toxicity and secondary reactivity. In this paper, we report that the distribution of monohydroxylated intermediates (m-, p- and o-) formed during the photocatalytic oxidation of aromatic compounds changes with the variation of reaction conditions, such as O(2) partial pressure and substrate concentration. By detailed product analysis, theoretical calculation, and oxygen isotope labeling experiments, we show that these changes are due to the selective reduction of HO-adduct radicals (the precursors of hydroxylated intermediates) by conduction band electrons (e(cb)(-)) back to the original substrate, that is, p- and o-HO-adduct radicals are more susceptible to e(cb)(-) than the m- one. Our experiments give an example that, even under oxidative conditions, the yield distribution of isomeric intermediates can be modulated by e(cb)(-)-initiated reduction. This study also illustrates that the unique redox characteristics of photocatalysis, that is, both oxidation and reduction reactions take place on or near the surface of a single nanoparticle, can provide opportunities for the reaction control.

Selective Oxidation Using Flame Aerosol Synthesized Iron and Vanadium-Doped Nano-TiO2

Selective photocatalytic oxidation of 1-phenyl ethanol to acetophenone using titanium dioxide (TiO2) raw and doped with Fe or V, prepared by flame aerosol deposition method, was investigated. The effects of metal doping on crystal phase and morphology of the synthesized nanostructured TiO2were analyzed using XRD, TEM, Raman spectroscopy, and BET nitrogen adsorbed surface area measurement. The increase in the concentration of V and Fe reduced the crystalline structure and the anatase-to-rutile ratios of the synthesized TiO2. Synthesized TiO2became fine amorphous powder as the Fe and V concentrations were increased to 3 and 5%, respectively. Doping V and Fe to TiO2synthesized by the flame aerosol increased photocatalytic activity by 6 folds and 2.5 folds, respectively, compared to that of pure TiO2. It was found that an optimal doping concentration for Fe and V were 0.5% and 3%, respectively. The type and concentration of the metal dopants and the method used to add the dopant to the TiO2are critical parameters for enhancing the activity of the resulting photocatalyst. The effects of solvents on the photocatalytic reaction were also investigated by using both water and acetonitrile as the reaction medium.

A model for prediction of product distributions for the reactions of phenol derivatives with hydroxyl radicals

In this study, with the intention of estimating the photocatalytic or photodegradation rates and finding certain predictors to be used for the determination of the most probable reaction path and the primary intermediate, the reactions of (*)OH radicals with 11 phenol derivatives including benzene were modeled. For 43 possible reaction routes, calculations of the geometric parameters, the electronic and thermodynamic properties of the reactants, the product radicals and the transition state complexes were performed with the semiempirical PM3 and DFT/B3LYP/6-31G(*) methods. The solvation effects were computed using COSMO as the solvation model. Based on the results of quantum mechanical calculations, the rate constants, the branching ratios and the product distributions of all the possible reaction paths were calculated by means of the transition state theory. Three predictors were determined for the prediction of the most probable transition state and the reaction path. The differences in the reaction rates were explained in terms of the presence of hydrogen bonds in the transition state complexes and the entropy effects. Finally the results obtained were compared with the available experimental data in order to assess the reliability of the proposed model.

The hydrogen peroxide-assisted photocatalytic degradation of alachlor in TiO2 suspensions

Photocatalytic degradations of alachlor in TiO2 suspensions with and without the use of hydrogen peroxide were studied using two different monochromatic UV irradiations (300 and 350 nm). Direct photolysis of alachlor was a rather slow process, but the addition of TiO2 enhanced the reaction rates by 12 and 26 times using 300 and 350 nm UV irradiation, respectively. The results showed that a low H2O2 dosage in photocatalysis using 300 nm UV would enhance the rates by 3.3 times, but an overdose of H2O2 will retard the rate due to the hydroxyl radicals are consumed. However, this process is impracticable at 350 nm due to the absorption characteristic of H2O2. A neutral initial pH level was found to favor the H2O2 assisted photocatalysis at 300 nm UV illumination. Eleven major intermediates were identified by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) and MS/MS. The major degradation mechanisms of H2O2-assisted alachlor photocatalysis include dechlorination, dealkylation, hydroxylation, cyclization, scission of C-O bond, and N-dealkylation. Bell-shaped evolution profiles of different intermediates were observed. Degradation pathways were proposed accordingly to illustrate series of degradation steps. The TOC analysis revealed the different stages of the reaction.